This invention relates to the structure of a piezo-resonator such as used in a clock signal generating circuit in a variety of digital systems.
FIG. 8 is a plane view showing a strip-shaped energy-confined type piezoelectric resonator element 10. In the figure, 11 and 12 denote electrodes arranged on both faces of a piezoelectric plate 13. 14 and 15 denote dummy electrodes for facilitating attachment of the piezoelectric resonator element 10 to terminals or the like, and which need not be provided. Both ends of the electrodes 11 and 12 face each other through the piezoelectric plate 13, whereas the other ends are led to the ends of the piezoelectric plate 13, respectively.
FIG. 9 shows an example of the structure of a conventional piezo-resonator employing the strip-formed piezoelectric resonator element 10 mentioned above. A supporting board 20 is made up of a printed board or the like with conductive patterns 21 and 22 formed on an insulating board. The piezoelectric resonator element 10 is fixed on the supporting board 20 by soldering the electrodes 11 and 12 and the dummy electrodes 14 and 15 to the conductive patterns 21 and 22 of the supporting board 20, respectively, and respective terminals 30 and 40 soldered to lower portions of the conductive patterns 21 and 22.
After this procedure, the piezo-resonator is coated with an outer resin 60 such as epoxy resin under the state that a gap is provided to the periphery of a vibrating portion of the piezoelectric resonator element 10. Numeral 50 denotes solder.
However, the above mentioned structure has the following drawbacks.
(1). The many junctions due to the necessity of joining the electrodes 11 and 12 of the piezoelectric resonator element 10 and the terminals 30 and 40 to the supporting board 20 complicate the assembly process.
(2). Positioning is difficult when mounting the piezoelectric resonator element 10, the terminals 30 and 40, etc. on the supporting board 20.
(3). Since the outer resin 60 contracts when it is heated to harden, stress is applied to the piezoelectric resonator element 10 and its characteristics as a piezo-resonator deteriorate.
(4). Solder-leakage may occur when the piezoelectric resonator element 10 is soldered to the conductive patterns 21 and 22 and lead the solder to attach to the vibrating portion. This excessive solder not only causes the fluctuation of a resonance frequency by suppressing the main vibration of the piezoelectric resonator element 10 but also an increase of a resonance resistance, and the generation of unnecessary spurious radiation or the like.